1. Technical Field
This disclosure relates to a sheet conveying device that conveys sheet such as paper and an image forming apparatus that incorporates the sheet conveying device.
2. Related Art
Image forming apparatus includes copier, printer, facsimile machine, plotter, and multifunctional apparatus including at least two functions of the copier, the printer, the facsimile machine, and the plotter. Such image forming apparatus is currently demanded on the market to perform a paper handling operation of a wide variety of sheets of paper different in type, thickness, size, and the like. Specifically, printers are expected to be faster while handling the above-described variety of sheets of paper. Moreover, there is an increasing demand of the market for image position accuracy.
At present, as a paper position correcting mechanism for enhancing the image position accuracy, a known skew correcting mechanism corrects skew in which a sheet is conveyed while diagonally displaced with respect to a sheet conveying direction.
Another known shift mechanism corrects positions of an image and paper in a sheet width direction (a main scanning direction) orthogonal to the sheet conveying direction.
One method of the skew correcting mechanism is a nip method in which a nip is formed by forming one of a registration roller pair as a rubber roller and the other as a metal roller and diagonal displacement is corrected by abutting a leading end of paper against the nip.
An example of the skew correcting mechanism discloses a method in which a drive roller of each of registration roller pair and each of gate members, against which a leading end of paper abuts, are formed integrally.
In this method, after abutting the leading end of the paper against the gate members to correct the diagonal displacement, the rollers of the registration roller pair are rotated to convey the paper and the gate members are rotated in synchronization with rotation of the registration roller pair to move aside from a sheet conveying path.
The gate members with respect to a subsequent sheet can be repositioned in a short time by a single turn of the registration roller pair. Therefore, skew correction (diagonal displacement correction) of the sheets conveyed at high speed can be performed and intervals between the conveyed sheets can be reduced.
Furthermore, each of the gate members has a sheet conveying guide portion. When the sheet is convened to a conveyance roller pair disposed downstream from the registration roller pair in the sheet conveying direction, a driven roller of the registration roller pair separates form a drive roller thereof.
After a trailing end of the sheet passes between the two rollers of the registration roller pair, the driven roller comes into contact with the drive roller again.
By employing a method in which the two rollers of the registration roller pair contact with pressure, are rotated, and the gate member is repositioned, high-speed skew correction can be performed irrespective of length of the sheet.
In a shift mechanism, a sensor that detects an end of the sheet is provided to the sheet conveying path, so that a positional displacement of the sheet and an image from each other is calculated. Based on detection results obtained by the calculation, a skew correcting mechanism is moved in the main scanning direction to align the image.